Automatic volume control



Oct. 23, 1934. R. AUBERT AUTOMATIC VOLUME CONTROL Filecil May 4, 1951 burin INVENToR ROGER A BERT BY ,www

1 ATTORNEY Patented Oct. 23, 1934 1,978,184 AUTOMATIC voLUME'ooN'rRoL Roger Aubert, Paris, France, assigner to Com-V pagnie Generale de Telcgraphie Sans Fil, a

corporation of France Application May- 4, 1931, Serial No. 534,869

In France May 12, 1930 N claims. (ci. 25o-2o) The present invention relates to improvementsl in circuit arrangements adapted to regulate the sensitivity of amplifiers.`

Systems generally used for insuring an autot .p 5 matic variation of the `sensitivityof an amplifier are Well known'in lthe prior art. These systems rrcan bedividedinto two chief classes.l In theiirst class the polarizing, or biasing, potential of the grid-of the amplifier tubes is directly acted upon ,leso asto regulate the amplification of the system by the `convenient choice ofthe working points `of `the tubes. `In the second class the plateimpedance of triodes is shunted by the filamentplate-circuit of a supplemental triode whose inj 15 ternal resistance is varied by regulation `of its grid potential, for instance. The effective amplioation of the stage is thus set to" the gdesred nvalue. s f

rNow, both of `these two systems involve certain l inconveniences. vIn the former, with the signal `and the control system both acting upon one and the same electrode, there occurs always detection t and distortion of the signal, the latter being so much more marked the stronger the signal. In

25 thesecond class, the signal and the control sys- `tern act upon two different electrodes, and the distortion of the signal may be reduced to zero by the judicious choice of the shunt tube. `How ever, the variation in amplification permitted by the system is diminished owing to the low internal resistance of the shunt tube which is never of 'zero`value`.` s

" The system which forms thecbjectof rthe present invention', and which `represents an improve- ,p ment upon that disclosed in a prior co-pending application, permits a very great variation in amplification, while at the same time avoiding the distortion of the signal. `Brieiiy,it comprises a potentiometer coupling associated with a` coml 4,0 plete compensation of the residual effect.

In the drawing, l y Fig. 1 shows an amplifier arrangement' without the `present invention, l f

Fig. 2 shows the arrangementof Fig. 1 embodying the `present invention,

Fig. 2a. is a modified form of the invention.

Fig. 3 shows still another modification,

Fig. 4 schematically shows a receiving system embodying a preferred form of the invention.

, In order to facilitate the understanding of the operation` of the system, Fig. 1 shows the provision of a` potentiometer coupling device without s compensation of the residual effect. The coumpling between the inputterminals 1, 2 andthe 55. output terminals 3, 4 of an amplifier is insured across an assembly of fixed resistances 5 and triode tubes `6. The system controlling the arnplifier acts at 7 upon the grid potential of tubes 6 so as to modify their internal resistance. When `(l0 the internal resistance of the tubes 6 is high compared with resistance 5, the ratiobetween the potentials prevailing across 3, 4 and 1, 2 is close to unity, and may be expressed as follows:

am 1 U 1, 2: s where U 3, 4 is the potential difference between points 3 and 4, and U 1, 2 is the potential difference between points 1, 2. y s V When the internal resistance of tubes 6 is equal top the relationship between the potentials across 3,4and1,2is: p

. s U 1, 2 R-l-p where Ris the magnitude of the resistor 5.

The maximum amplification variationis thus equal to:

Ripmm 2l-.W pmn. n The resistance pmin. being given, and since the resistance R should not be too high (for this would cause tube 6 to operate under an unduly low plate potential), the maximum amplication variation is limited. 'Ihe scheme shown in Fig. 2 is adapted to neutralize the residual effect of resistance p.

`The system is particularly adapted to amplifiers with a symmetric circuit arrangement. An embodiment thereof as applied to an amplifier as stated is shown schematically in Fig.2.

With this end in view two high resistances 8 are. disposed between points 1, 4 and 2, 3 of the system, connection with the next stage being then established at 3', 4. The rough outline to be given hereinafter will facilitate the understanding of the operation ofthe system. When tube 6 has its lowest internal resistance pmin., points 1 and 2 ,respectively are at potcntials-l-Uand U, and

the points 3 and 4 at potentials The resistances 8 being always arranged between two points having potentials (-F U and 1g) for the first, and

Y and its!) for the second one, two symmetric points 3 and 4 will be found upon these resistances which will be at zero ,potential and for which the residual amplification will be of zero value. If the resistances 8 are high compared with resistances 5, the maximumampliiication will be but slightly `affe'cted. At all events, however, the variation of samplification will be as high as may be desired.

Fig. `3 shows another embodiment of the system. The sum total of theresistances 9 and r10 of Fig. 3 corresponds to resistances 8, Fig. 2, resistances 9 being equal to resistances 5 andresistance 10 being high compared with resistances/ 5, so as to preserve a high maximum amplication. The two resistances 18 connected between (across) the terminals of resistances 9 land the midpoint of the system are equal to the minimum internal resistance of the triodes. In order that these systems may be stable it is'evidently necessary that the internal resistance of the triodes should grow when the strength of the signal falls off, and vice versa. In other words, the negative potential applied to the grids must increase when theuvolume of the signal falls off.

This' purpose may be obtained by detecting (rectifying) the signal, and by amplifying it in a suitable manner (for instance, by a direct current ampliiier) until the desired value and sense of variation is insured. The flow of the current 5 through the plate resistance of a direct current 'amplier tube will be used to polarize the grids.

Fig. 4 shows by way of example a mode of application of the invention to the regulation of an ampliiier MF. The regulator system like the one shown in Fig. 2 of which the input terminals 1, 2 and the output terminals 3', 4 are indicated is inserted between thestages of medium frequency amplification schematically indicated by the boxes MF and MF, the output tubes of the 'former 11', 11 and the input tubes of the second l2, 12 being diagrammatically indicated by their grid and plate electrodes. B represents the plate supply of the tubes, and'C the grid biasing source.

`The potential actuatingthe regulator tubes is furnished from the direct current ampliiier represented by the relay tubes R, R coupled by resistance with plate counter batteries, and excited by the detected current at the output end of the amplifier MF' in line with a well-known scheme which is but partly shownin Fig. 4.

Themodus operandi of the'device is as follows: The incoming signal is amplified by amplifier MF, and then detected. Part of the detected-current is supplied to the direct current amplifier which constitutes means adapted to make the po- Atential'dependent'only upon the carrier wave with preclusion of modulation, and which at the output end results in an amplied potential adapted to Ystrongly polarize the tubes 6. These tubes shunt one stage of amplification 11. When the .incoming carrier Wave Varies vin one sense-or the `other the resistance of the tubes 6 Varies 1n sultplaced by a tetrode or pentode whose characteristics occasionally are of greater'advantage.

It is evident that the circuit arrangements hereinbefore disclosed are capable of a number of modications without departing from the I basic spirit of the invention. For instance, the plates' of tubes 6 may be Vfurnished with potential by land 2, 3, 4 lor3, 4 bythe aid of blocking impedance, or directly by the system itself as frequency,

shown in Fig. 4. While the system has here been shown as comprising resistances, the latter could be replaced by reactance, either inductive or capacitive, at least for the impedances 8 of Fig. 2, and 18, 9, 10 of Fig. 3 as shown in Fig. 2a.

What Iy claim is:

1. In a receiver, cascaded amplifiers of superaudible frequency, each thereof comprising a pair of tubes in push-pull, means for detection connected with the output of the amplifiers, a coupling means inserted in the cascade and comprisinga pair of tubes in parallel whose plates are associated with the plates of the amplifier below, an assembly of symmetric impedances interconnecting each plate of the preceding amplier stage with the plate of an opposite coupling tube, connections between points of 'each Yof these irnpedances which are at alternating zero potential .when the internal impedances ofthe said coupling tubes are at a minimum and the input of the next amplifying stage and means for applying the output currents of the detection means to the grids of the said coupling tubes.

2. In a receiver, a cascade of amplifiers of high frequency, each comprising a pair of tubes in push-pull, means for detection -connected with the output of the amplifiers, a coupling element inserted in the cascade and comprising a .pair of tubes in parallel whose plates are associated with.

the plates of the preceding amplifier stage, an assembly of symmetric impedances interconnecting each plate of the preceding amplifier stage with the plate of an opposite coupling tube, other impedances vinterconnecting the plates of the pre-.110

ceding amplifier stage, connections rbetween points'of each of the said first-mentioned impedances which are at alternating zero potential when the internal impedances of the said coupling tubes are at a minimum and the input of the next amplifier stage, and means for feeding the output current of the detection means to the grids ofthe said coupling tubes.

l 3. In areceiver, a cascadegof ampliers of vhigh frequency, comprising each a pair of -push-.pull tubes, means for detection connected with the output of the amplifiers, a coupling element inserted in the cascade and comprising a pair of tubesfin parallel whose `plates are associated with the plates of the preceding amplifier stage, an assembly of symmetric impedances interconnecting each plate of the'preceding amplifier .stage with the plate of an opposite coupling tube, connections between points of each of these impedances which are at alternating Zero :potentiall when the internal impedances of the saidcoupling tubes are at a minimum, and the input of the next amplifier stage, means for amplification of the ycurrent at'the outputend of the detection means, and means for feeding 'the .amplified current tov the grids of the said coupling tubes.

4. Ina receiver, a cascade of amplifiers of high each vcomprising `a -pair of push-pull tubes, means for Idetection connected -with the output of the ampliiiers,acoupling element serted in the cascade and comprising a pair of tubes excited in parallel whose plates are associated with the plates-of `the preceding amplifier stage, an assembly of symmetric impedances interconnecting each plate of the preceding ampliyiier stage with the plate of an opposite vcoupling tube, other impedances interconnecting theplates of the preceding amplifier stage, third impedances `inserted between each -plate of Athe preceding in-y ico

amplier stage andthe Aplate of the coupling tube '150 on the same side, connections between points of each of the said first-mentioned impedances which are at alternatingzero potential when the internal impedances of the said coupling tubes are at a minimum and the input of the next amplifier stage, and means for feeding the output current of the detection means to the grids of the said coupling tubes.

5. In an anti-fading receiver, amplifiers of high frequency each comprising a pair of push-pull tubes, means for detection connected with the output of the amplifiers, a coupling element inserted in the cascade and comprising a pair of tubes excited in parallel whose plates are asso'. ciated with the plates of the preceding amplier stage, an assembly of symmetric impedances interconnecting each plate of the preceding amplifier stage with the plate of an opposite coupling tube, other impedances interconnecting the plates of the preceding amplifier stage, third impedances inserted between each plate of the preceding amplier stage and the plate of the coupling tube being on the same side, each of the said first mentioned impedances being equal to the sum total of one of the said third impedances and the internal resistance of a coupling tube, connections between the points of the said .firstmentioned impedances separated from the plate by the impedance equal to the said third impedance and the input of the following ampliiier stage, and means for feeding the output current of the detection means to the grids of the said coupling tubes.

ROGER AUBERT; 

